Recent years have seen proposals of techniques for identifying a left-behind object or a person standing still for a certain period of time or longer (for example, refer to PTL 1) such as in video surveillance. In PTL 1, motions in a scene are analyzed at multiple time scales, and a long-term background model and a short-term background model are compared. Through this comparison, pixels corresponding mainly to a static background part, a dynamic foreground part, and a left-behind object standing still over a certain period of time, of the scene are differentiated.